Low pour point lubricants



Patented Mar. 2, 1954 2,671,051 LOW POUR POINT LUBRICANTS Robert J. Moore, Oakland Calif., assignor to Shell Development Company, Emeryville, Calif., a

corporation of Delaware N Drawing. Application September 4, 1951,

Serial No. 245,097 11 Claims. (Cl. 196-151) This invention is directed to the improvement of lubricating compositions. More specifically, it refers to lubricants having improved pour points and other properties.

Mineral lubricating oils usually comprise hydrocarbons containing a minor amount of waxy components. Waxes are regarded arbitrarily as hydrocarbons having melting points above about '0 C. The presence of certain types of waxes in mineral lubricating oils limits the use of the latter, especially at such temperatures that the waxes commence to crystallize from the oil. The temperature at which the waxes crystallize from a given oil and form an immobile matrix under standardized test procedures is termed the pour point of the oil.

Waxes have recently been identified as existing in several well-defined structural types. The most commonly employed for many industrial purposes are the straight chain waxes normally called paraffin wax. The second type comprises isoparaffins and/or molecules consisting of cyoloparaifins attached to moderately long straight chains and are ordinarily termed amorphous or microcrystalline waxes. A third type which is not 'as clearly defined in structure appears to be partly naphthenic and partly aromatic in character (e. g., alkyl tetralins). Finally, an appreciable portion of the higher boilingmaterials comprises aromatic Waxes (e. g., alkyl naphthalenes, etc.) It has been found that each of these particular types of waxes has a specific effect upon the pour point of any oil in which it exists. The most serious effect with respect to pour point is caused by the presence of straight chain parafiin waxes. This appears to be due to the fact that these straight chain waxes crystallize in large multi-layered hexagonal plates, and that the network of such plates holds the oil and prevents its mobility. The ability of paraffin waxes to crystallize in this manner appears to be due to the fact that all portions of the wax molecules are highly crystalline in character, and thus promote the formation of a chain type of crystal lattice. As opposed to this, electron micrographs have shown that as the wax molecule departs farther and farther from the straight chain paraflin structure, the highly crystalline nature of the molecule progressively disappears. Consequently, these non-paraifin waxes have a diminished deleterious effect upon the pour point of any oil containing them.

It is an object of the present invention to improve the properties of mineral lubricating oils. It is another object of the invention to improve lubricating oils containing straight chain parafiin waxes. Another object of this invention comprises the minimizing of the deleterious effects of such waxes when present in mineral lubricants. Other objects will become apparent during the following discussion.

I Now in accordance with this invention, it has been found that the pour point of waxy lubricating oils comprising medium or low viscosity oils containing normal parafiin waxes can be lowered by the addition thereto of a critical proportion of an extraneous hydrocarbon wax, the latter bearing a cyclic end group attached to an aliphatic hydrocarbon chain. Still in accordance with this invention, it has been found that optimum results are obtained when this extraneous wax comprises average hydrocarbon chains which do not differ from the average normal paraffin wax chain length by more than about 4 carbon atoms.

Isoparaffins and naphthenes exhibit reduced crystallization tendencies in mineral lubricating oils. These tendencies are minimized, apparently due to the non-crystalline or low crystalline forces exhibited by the cyclic or branched portions of the molecules. 0n the basis of observations made, it has been concluded that naphthenic Waxes crystallize in mono-molecular plates with the straight chain portions of the molecule more or less perpendicular to the plate surface. The ring or naphthene portion attached to the end of each chain would be oriented in the crystal surface with molecules arranged so that both crystal surfaces would comprise the non-crystalline or ring portions of each molecule. With this type of exterior surface, the forces holding the crystallites together are much less than those found with a surface of methyl groups presented byfthe crystals of n-paraffins. Indeed, it has been found that lubricating oils containing naphthenic or other non-straight chain waxes form grease-like mixtures rather than solids. That is, it would appear that the non-crystalline heads of the naphthenic or aromatic waxes cannot build up multi-layer crystals such as the three dimensional lattices of the parafiin waxes.

Hence, it is not possible to obtain a rigid solid as was obtained with the latter.

While the present invention applies to mineral SSU at F. Hence the invention applies specifically to mineral lubricating oils having viscosities between about 50 and about 250 SSU at 100 F., and preferably to oils having viscosities between about 75 and 200 SSU at 100 The source of the lubricating oil does not comprise an essential feature of the present invention. Ordi narily it will be a petroleum oil which contains an inherent proportion of normal paraffin waxes, that is, normal paraflin hydrocarbons which normally tend to crystallize from the oil at a temperature above the desired pour point of the oil. However, at times it may comprise a syn thetic mixture of an originally non-waxy oil to which normal paramn waxes have been added.

The normal paramn waxespresent in the lubricants of this invention (usually in amounts between about 0.25% and about 5% by weight, based on the lubricant) comprise those having melting points above 0 C. and usually contain atleast 29 carbon atoms per molecule. The general range of normal parafiin waxes having from about to about carbon atoms per molecule show especially high response to the additives used in accordance with the present invention.

In accordance with this invention, the pour points of oils containing such normal paraflin wax are substantially depressed by the addition thereto of at least one extraneous hydrocarbon wax bearing a cyclic end group on an aliphatic hydrocarbon chain. A further requirement is that such extraneous wax bears an average aliphatic hydrocarbon chain differing by not more than about 4 carbon atoms (preferably not more than about 3 carbon atoms) from the average chain length of the normal paraffin waxes responsible for the undesirably high pour point. A still further requirement of this invention comprises the presence of from about to about 150% (preferably -125%), based on the weight of the normal paraffin waxes, of this extraneous hydrocarbon wax. If greater or less amounts of added wax are employed, it has been found that any pour point depression is either nonexistent or that the added wax actually raises the original pour point. These extraneous hydrocarbon waxes comprise especially naphthenic waxes and aromatic waxes. monoor dicyclic structures bearing at least one long aliphatic side chain. They may also comprise one or more short chain substituents attached to other points of the cyclic nucleus. Due to the manner in which they are ordinarily obtained (which will be disclosed hereinafter), they are not usually identifiable as a particular species. Instead, they usually comprise a closely related pair or group of species especially useful for addition to waxy oils within the chain length limitations referred to hereinbefore. It will be understood, however, that single species may be used.

While the extraneous hydrocarbonwaxes which are utilized for addition to normally waxy lubricants may be synthesized, they are preferably obtained from natural sources by fractionation procedures enabling the isolation of the desired type and elimination of less desirable components. The isolation of aromatic or naphthenic waxes may be, for example, from either distillate waxes or residual waxes. In the case of the distillate waxes, use is made of the differences in solubility of various heavy oil components in two solvents, namely acetone and methyl ethyl ketone at relatively low temperatures. However, a distinctive difierence in solubility occurs only when the accompanying oil components of similar molecular weightare compared. Therefore, the first preferred step for Ordinarily these are the separation of such waxes comprises the fractional distillation of a raw lubricating oil into narrow boiling cuts. The differences in solubility become more pronounced the smaller the spread of the molecular size. Hence, the narrower the cut is made, the sharper will be the subsequent separation. .At temperatures below about 50 C., acetone dissolves only the highly aromatic components of the molecular weight range here involved, namely, between about 250 and about .700. Therefore, by cooling an acetone solution containing the mixed types of waxes to between '50 and 6G C., all of the components other than the aromatic waxes become insoluble in acetone and consequently can be separatedfrom the aromatics by filtration, due to the fact that the main part of it is solid at that low temperature.

For'the fractionation of the remaining types of waxes, acetone cannot be used since its selectivity is too small. Therefore, the filter cake from the first separation is freed from acetone and dissolved in methyl ethyl ketone or a similar ketone. Upon cooling this solution to a temperature between -50and -60 C., the straight chain parafiin hydrocarbons and isoor cyclic paraffins crystallize. These are filtered off, thus leaving the partially aromatic and partially naphthenic components dissolved in cold methyl ethyl ketone. The solid mixture "of isoparafiins and naphthenic waxes .is again dissolved in a fresh quantity of methyl ethyl ketone, taking particular care to utiliaeonly :narrow boiling distillate cuts of the waxes. These solutions can then be progressively cooled and the crystallizing waxes periodically removed. The crystals are tested for refractive index in order to determine the temperature at which further crystallizations should be carried out so as to effect separation of all of the normal paraifin waxes from the isoparainns and naphthenes.

Ordinarily the extraneous waxes to be employed for addition to waxy lubricating oils are obtained by fractionation of residual waxes. These are the waxes which remain (usually in combination with asphalt and heavy lubricatin oil) after distillation of lower boiling material such as gasoline, kerosene, gasoil, and waxy lubricating oils. A typical separation of this character will now be described:

An East Texas crude oil was topped, by distilling off the lighter fractions of hydrocarbons at atmospheric pressure, the remainder being recovered as a straight'run residue or reduced crude. This straight run residue was then subjected to vacuum distillation to recover lubrieating oil base stock contained therein, as one or more distillate fractions, including all material which was removable at about 650 Rand mm. of mercury absolute pressure and obtaining therefrom a short residue waxy material, representing a maximum of about 30% of the straight run residue. About'd()% of the short residue was removed as asphaltic material :by propane deasphalting, leaving a deasphalted short residue which was subjected to extensive extraction with phenol to removezaromatics and polar materials which are deleterious to lubricating oils. About half of the deasphalted short residue was separated in the phenol solvent extraction process as a waxy raffinate. About half of this waxy rafiinate was recovered as a high viscosity, lubricating bright stock, by dissolving the raffinate in a dewaxing :solvent mixture :of methyl :ethyl ketone, benzene and toluene, chill- 'ing to about F. to precipitate the waxesand filtering the wax from the oil. The wax was thoroughly washed on the filter, after which it was recovered therefrom as an oily wax, the socalled short residue slack wax, which may be termed short residue crude wax. The crude wax had the following properties: Specific gravity (/4 C.)0.8936, at 100/4 C.-0.8176; refractive index, 90 C./D1.452; color (ASTM D155-45T) at 100 C.4 (diluted with kerosene according to ASTM method for petrolatum -darker than 8 color); dropping point (ASTM D566-42) F.1'71; methyl ethyl ketone cloud point-154 F.

, The crude wax was fractionated into ten fractions by distillation in a molecular still, thereby producing ten fractions of the wax according .to molecular size or weight, since the boiling points of the waxes are approximately the same for waxes of the same molecular weight, although of difierent types or structure. The straightchain parafilns were separated from the other components of the various fractions by crystalline molecular complex formation with urea, using a saturated aqueous solution of urea to contact a methyl isobutyl ketone solution of the .wax fraction. The remainder of each fraction was separated by chromatographic adsorption and sequential elution separation into three type fractions, namely, (1) an isoparaffinic/naphthenic fraction, (2) a naphthenic/aromatic fraction and (3) an aromatic/resin fraction.

I The examples which follow illustrate the compositions and utility of the present invention.

Example I. In order to demonstrate the eiiect of aromatic waxes on the pour point of waxy lubricating oils, the following compositions were prepared. Similar portions of a mineral lubricating oil having a pour point of 40 F. and containing substantially no waxy components were modified by the' addition of 0.5% by weight of a normal parafiln wax having an average of 27 carbon atoms per molecule and a melting point of 138 F. to yield waxy oils having pour points of -20 F. An equal amount (0.5%) of various aromatic waxes was added to each of the waxy oils and the pour points of the resulting compositions were determined. Table I contains the data obtained; the data show that the addition of a particular aromatic wax closely in chain length of the aliphatic side chain thereof to the average chain length of the normal paraflin wax resulted in a substantial decrease in the pour point.

Table EFFECT OF AROMATIC WAXES 0N POUR POINT OF WAXY LUBRICATING OIL 1 No aromatic wax.

Example II.Similar compositions were prepared utilizing the same oil and normal paraffin wax but wherein the Waxy oil was modified with naphthenic waxes. Pertinent data relative thereto are given in Table II.

corresponding 6 'Table II POINT Carbon Atoms in Aliphatic Chain of N aalithene Melting Point of Naphthene Wax, F.

(I) 154 4:2 8 a1 -a0 1 N0 naphthene wax.

It will be seen from these data that it was necessary to use a naphthenic wax closely corresponding in side chain length to the average normal paraffin wax molecular chain in order to obtain an appreciable pour point depression. In order to illustrate the critical nature of the invention in this respect, a much higher molecular weight material (Sample B) was also used. When such a material was employed, the addi tion of this high molecular weight material actually caused a substantial increase (40 F.) in pour point rather than the desired decrease, although this naphthenic wax had a melting point only about 16 F. higher than the melting point of the paraffin wax.

Example III.In order still further to illustrate the necessity for coordinating the aliphatic side chain length with the average normal paraffin chain length, a normal parafiin having an average chain length of 32 carbon atoms and a melting point of about 156 F. was dispersed in other portions of the same non-waxy lubricating oil employed in Examples I and II. "To this combination, the same naphthenic wax which gave a poor result in Sample B of Example II (Table II) was added with the result that there was at 75 F. depression in pour point of the oil. The reason for the beneficial result (opposite to its use in Sample B, Table II) being obtained in this case is due to the fact that the normal paraffin wax present in this instance more closely corresponded in chain length to the extraneous naphthenic wax than was true in the case of Sample B, Example II (Table II).

- Table III Cloud I Point,

Pour Point, F.

Sample 1 No naphthene wax.

were added varying amounts of a naphthenic wax having a melting point of 48 F'. This was a portion of the same wax used in Sample D of Example I. The results of pour point determinations, given in Table IV, show that it was necessary to use by weight based on the weight of the normal parafiin wax, of the naphthenic wax in order to obtain a pour point depression of 35 Table IV Percent 'Pour Sample Naphthenic Point,

Wax F.

I claim as my invention:

1. A normally fluid lubricating composition comprising a major amount of a waxy hydrocarbon lubricating oil having a viscosity between about 50 and about 250 'SSU at 100 F., the waxy portions of said oil predominating in normal aliphatic hydrocarbon waxes having an average chain length of at least 20 carbon atoms per molecule and as a pour point depressant therefor from about 75% to about 150% based on the weight of said waxes of at least one extraneous hydrocarbon wax bearing a cyclic end group on an aliphatic hydrocarbon chain, the latter differing from the average normal aliphatic hydrocarbon wax chain length by no more than about 4 carbon atoms.

2. Composition according to claim 1 wherein the normal aliphatic waxes are present in an amount from about 0.25% to about 5% based on the weight of the lubricating oil.

'3. A normally fluid lubricating composition comprising a major amount of a waxy hydrocarbon lubricating oil having a Viscosity between about 50 and about 250 SSU at 100 the waxy portions of said oil predominating in normal aliphatic hydrocarbon waxes having a chain length of at least carbon atoms per molecule and as a pour point depressant therefor, from about 75% to about 150 based on the weight of said waxes of at least one extraneous naphthenic wax bearing a naphthenic end group having an aliphatic hydrocarbon side chain, the latter difiering from the average normal aliphatic hydrocarbon wax chain length by no more than about 4 carbon atoms.

4. A composition according to claim 3 wherein the naphthenic end group is a mono-cyclic naphthene group.

5.- .A composition according to claim 3 wherein the naphthenic end group is a dicyclic naphthenic roup. 1

-6. A normally fluid lubricating composition comprising a major amount of a waxy hydrocar bon lubricating oil having a viscosity between about and about 250 SSU at l'00-F.-, the waxy portions of said oil predominating in normal aliphatic hydrocarbon waxes having a chain length of at least 20'carbon atoms per molecule and as a pour point depressant therefor, from about to'about-150%, based on the weight-of said waxes of at least one extraneous aromatic wax bearing an aromatic end group having an aliphatic :hydrocarbon sidechain, the latter differing from :the average normal aliphatic hydrocarbon wax chain length by no more thanabout 4 carbon atoms.

7. A composition according to claim 6 wherein the aromatic end group is a dicyclic aromatic group.

8. A normally fluid lubricating composition comprising a'maior amount of a waxy lubricating oil having 'a'viscosity between about 50 and about 2505'SSU at F., the waxy portions of said'oil predominating in normal aliphatic hydrocarbon waxes having an average chain length of between about 20 and about 40 carbon atoms per molecule and as a pour point depressant therefor, from about '7 5% to about 150 based on the weight of said waxes of at least one extraneous hydrocarbon wax bearing a cyclic end group having an aliphatic hydrocarbon chain, the latter having a chain length difiering no more than about 4 car-'- bon atoms from the average chain length of the normal aliphatic hydrocarbon waxes.

9. A composition according to claim '7 wherein the aliphatic hydrocarbon chain'of the extraneous wax differs in average chain length by no more than about 3 carbon atoms from the average chain length of the aliphatic hydrocarbon waxes.

10. A composition according 'to claim '7 wherein the extraneous hydrocarbonwax is'present in an amount between about 85% and about based on the weight of the aliphatic hydrocarbon wax.

11. In a process for the depression of the pour point of a waxy mineral oil wherein the oil has a viscosity between about 50 and about 250 SSU at 159' F. and the waxy portions of said oil predominate in normal aliphatic hydrocarbon waxes having at least 20 carbon atoms per molecule, the steps comprising determining the average chain length of said waxes and-then adding to the waxy oil from about "15% to about based on the weight of said waxes, of at least one extraneous hydrocarbon wax bearing a cyclic end group having an aliphatic hydrocarbon chain, the latter having an average chain length differing by no more than about 4 carbon atoms from the average chain length of the normal aliphatic hydrocarbon waxes, the amount of extraneous 'wax added being 'suiiicient to substantially depress the pour point of the'waxy oil.

ROBERT J. MOORE.

References Cited in the file of this patent UNITED S'InTES PATENTS 

1. A NORMALLY FLUID LUBRICATING COMPOSITION COMPRISING A MAJOR AMOUNT OF A WAXY HYDROCARBON LUBRICATING OIL HAVING A VISCOSIY BETWEEN ABOUT 50 AND ABOUT 250 SSU AT 100* F., THE WAXY PORTIONS OF SAID OIL PREDOMINATING IN NORMAL ALIPHATIC HYDROCARBON WAXES HAVING AN AVERAGE CHAIN LENGTH OF AT LEAST 20 CARBON ATOMS PER MOLECULE AND AS A POUR POINT DEPRESSANT THEREFOR FROM ABOUT 75% TO ABOUT 150% BASED ON THE WEIGHT OF SAID WAXES OF AT LEAST ONE EXTRANEOUS HYDROCARBON WAX BEARING A CYCLIC END GROUP ON AN ALIPHATIC HYDROCARBON CHAIN, THE LATTER DIFFERING FROM THE AVERAGE NORMAL ALIPHATIC HYDROCARBON WAX CHAIN LENGTH BY NO MORE THAN ABOUT 4 CARBON ATOMS. 